Shafts having a worm formed onto it are used, for example, where a worm of a worm gear is to be driven by an electric motor, it being absolutely possible that the worm is formed directly onto the rotor shaft of the electric motor. The worm concerned can be an overhung worm as well as a worm mounted at both ends. In the latter case the diameter of the part of the shaft adjoining the one end of the worm can be larger than the part of the shaft adjoining the other end of the worm. However, it is also possible that there is an equal diameter of the shaft at both sides of the worm. Furthermore, the part of the shaft directly adjoining the one end and/or the other end of the shaft can have a diameter equal to the crown circle of the worm, but also can be different herefrom, for example larger.
If the root line diameter of the worm is smaller than the diameter of the part of the shaft adjoining the end, notch tensions can occur at the transition from the beginning of the worm into the adjacent part of the shaft and/or at the end of the worm to the part of the worm adjoined thereto. This can be noticed especially, if the worm is made by milling. In particular, in the latter case, it often happens that the crown circle of the worm corresponds directly to the diameter of the shaft or to the diameter of the part or the parts of the shaft directly adjoining the worm. The reason for this tension is that an abrupt transition occurs from the shaft diameter to the root line diameter. This can be noticed above all, when the worm is made by means of a disk milling machine.